One known electric power steering apparatus for turning steerable wheels of a vehicle includes a ball nut for transmitting force between an axially movable rack member and an electric motor. Upon actuation of the electric motor, the ball nut is driven to rotate relative to the rack member. The rotational force of the ball nut is transmitted to the rack member by balls to drive the rack member axially. Axial movement of the rack member effects turning movement of the steerable wheels. The advantages of this known apparatus include its compact size and high strength.
In another known electric power steering apparatus, an electric motor is connected with gearing which provides a gear reduction between an electric motor shaft and an output pinion meshed with an axially movable rack member. Rotation of the output pinion by the electric motor causes the rack member to move axially to turn the steerable wheels. The advantages of this known apparatus include a high gear reduction ratio and relatively low cost.
It is desirable to produce an electric power steering system which is compact in size, relatively inexpensive to produce, and which has high strength and a high gear reduction ratio.